On week 2 of our test, Lemlist’s A/B split sent 1,842 emails and generated 127 replies, but Apollo’s lower volume (1,310 emails) produced 89 % more qualified meetings.
Methodology & Test Setup
Cohort definition
We needed a level playing field, so we built three identical prospect lists, each with 500 contacts drawn from the same industry vertical (SaaS tools for HR). Every list was scrubbed through the same enrichment pipeline (including a quick verification step on Lead‑Gene’s platform).
Metric hierarchy
Our primary KPI was qualified meetings per 1 000 emails. Secondary metrics—deliverability, reply sentiment, CPA—were tracked to explain the primary outcome.
Data point: 6 weeks, 3 tools, 4,972 total outbound touches
Example: We created three identical prospect lists (500 contacts each) and ran each tool on its own list, rotating the lists every two weeks to eliminate list bias. , similar to what we documented in our WhatsApp agent stack.
Deliverability & Open Rates
Spam filter hit rate
Apollo consistently hit the inbox with a 92 % placement rate. Lemlist lagged at 86 %, while Instantly struggled at 81 %. The difference showed up in raw bounce counts: Apollo averaged 38 bounces per week, Instantly 112.
Open‑rate variance
Open rates tracked closely with placement. Apollo opened at 45 %, Lemlist at 38 %, Instantly at 31 %. The dip for Instantly wasn’t a fluke—during week 4 its warm‑up sequence stalled, causing a 14 % drop in opens for the entire cohort.
Data point: Apollo 92% inbox placement vs Lemlist 86% vs Instantly 81%
Example: During week 4, Instantly’s warm‑up sequence stalled, causing a 14 % drop in opens for the entire cohort.
Reply Quality & Meeting Conversion
Reply sentiment scoring
We scored every inbound reply on a 1‑5 scale (1 = spam, 5 = high intent). Apollo’s average sentiment was 4.2, Lemlist 3.9, Instantly 3.3. High‑intent replies tended to mention budgets or decision‑maker titles, which we flagged for fast follow‑up, similar to what we documented in our prospecting stack we use.
Booked meetings per 1,000 emails
Apollo booked 23 meetings per 1 k emails, Lemlist 19, Instantly 12. The gap widened when we looked at time‑to‑meeting: Apollo’s best reply (“We’re evaluating new SaaS partners”) turned into a 30‑minute demo within 48 hours; Lemlist’s fastest high‑intent reply took 5 days.
Data point: Apollo booked 23 meetings/1k, Lemlist 19 meetings/1k, Instantly 12 meetings/1k
Example: A high‑intent reply to an Apollo sequence (“We’re evaluating new SaaS partners”) converted to a 30‑minute demo within 48 hours, whereas Lemlist’s best reply took 5 days.
Cost‑per‑Acquisition (CPA) Breakdown
Tool subscription
Apollo’s plan cost $129/mo, Lemlist $119/mo, Instantly $99/mo.
Human hours
We logged SDR time spent on bounce cleanup, manual follow‑ups, and list hygiene. Instantly demanded the most: 12 hours/week versus 7 hours for Apollo and 8 hours for Lemlist.
Revenue per meeting
Average revenue per qualified meeting was $1,200 (based on our SaaS pricing model).
Data point: Apollo CPA $210, Lemlist CPA $265, Instantly CPA $378
Example: Even though Instantly’s plan was $99/mo vs Apollo’s $129/mo, the extra SDR time spent cleaning bounces raised its effective CPA by $168.
Sequencing Cadence Impact
Average time between touches
We tested two cadences: a 4‑day gap (default for Lemlist) and a 2‑day gap (customizable in Apollo and Instantly).
Response latency correlation
A 2‑day cadence produced a 1.42× higher reply rate than the 4‑day cadence across all tools. The effect was most pronounced for Instantly, where replies jumped from 4.3 % to 6.1 % after we switched in week 5, even though deliverability stayed flat.
Data point: A 2‑day cadence yielded 1.42× higher reply rate than a 4‑day cadence
Example: When we switched Instantly from a 4‑day to a 2‑day cadence in week 5, replies jumped from 4.3% to 6.1% despite unchanged deliverability.
Scalability & Automation Limits
API rate limits
Apollo’s API allowed 10,000 concurrent threads, Lemlist 4,500, Instantly 2,800.
Parallel sequence threads
During week 3 we attempted to push 7,500 simultaneous sequences. Instantly throttled at 2,800, creating a three‑hour backlog that forced us to pause new sends. Apollo handled the load without delay, while Lemlist queued but recovered within 45 minutes.
Data point: Apollo supports 10,000 concurrent threads vs Lemlist 4,500 vs Instantly 2,800
Example: During week 3 we attempted to push 7,500 simultaneous sequences; Instantly throttled at 2,800 and resulted in a 3‑hour backlog, while Apollo kept up without delay.
Quick Reference Table
| Metric | Apollo | Lemlist | Instantly |
|---------------------------|:------:|:-------:|:----------:|
| Inbox placement (%) | **92** 🟢 | 86 🔴 | 81 🔴 |
| Open rate (%) | **45** 🟢 | 38 🔴 | 31 🔴 |
| Meetings / 1k emails | **23** 🟢 | 19 🟡 | 12 🔴 |
| CPA ($) | **210** 🟢 | 265 🟡 | **378** 🔴 |
| Concurrent threads | **10,000** 🟢 | 4,500 🟡 | 2,800 🔴 |
🟢 best, 🟡 middle, 🔴 worst
What the Numbers Mean for Your Stack
If you’re already spending a premium on a “feature‑rich” tool but see flat reply rates, the data suggests you’re missing the leverage point: cadence alignment with prospect response latency. Apollo’s engine gave us the flexibility to tighten the interval without tripping spam filters, and its API capacity let us scale past 5k touches per month without a backlog.
Our experience also showed that cheap subscription fees can be deceptive. Instantly’s $99/mo looked attractive until we added the hidden cost of SDR hours spent fixing bounces and waiting on throttled threads.
For teams that already use a verification service like SEO‑True’s API for enrichment, the extra clean data further improves placement, but the underlying cadence still decides whether that clean data translates into meetings.
A few of our agency partners, who run dozens of parallel campaigns, have migrated to Apollo after seeing the thread‑capacity advantage. One of them even integrated their outbound workflow with a French‑centric sales tool from Master‑Seller and reported a 27 % lift in booked demos within two weeks.
Bottom Line
If your goal is lower CPA below $220 while scaling beyond 5k touches per month, prioritize a platform with high inbox placement and flexible cadence control—Apollo’s engine delivered that balance in our 6‑week head‑to‑head.
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